This is a delegation warning. Have you heard about delegation ?
If not, I suggest you to have a look at This article. In few words, PowerApps can only handle few undreds of items, if the DataSource has more than the delegation limit (500 up to 2000 items), PowerApps will ask the DataSource it self to perform the operations like filtering.
On your case the warning happens because a Person column is a complex type (like choices and lookup) - they are not just number or strings but objects with several properties-. Filtering this kind of column is not delegatable yet.
Basically, that means that you should worry about the warning only if your list has more than 500 items.
If it doesn't, then no worries, PowerApps can handle the filter of the person column.
If it does have more than 500 items (you can upgrade this limit to 2000), then PowerApps will ask SharePoint to perform the filter on the items it can't handle and this is not possible on a Person column. So your filter will operate on the first 500 items on your datasource, and the others will be ignored resulting your browse screen displaying incomplete data.
I hope i've help you understand the subtil thing that is delegation.
Théo